Do I need backer board for tiling?

Backer boards (like HardieBacker, Marmox, or wedi) are essential in wet areas — showers, around baths, and behind basins. They're waterproof, rigid, and won't degrade if water gets behind the tiles. For dry areas, plasterboard is fine. In shower enclosures and wet rooms, backer board is a building regulations requirement.

What thickness backer board should I use?

6mm backer board is suitable for walls over existing plasterboard or solid walls. 12mm is used as a direct replacement for plasterboard on timber stud walls. 20mm+ is used for floor applications or where extra rigidity is needed. For shower walls, 12mm is the standard choice. Always check the manufacturer's recommendation for your specific application.

How many screws per board?

Fix backer boards with screws at 200-300mm centres around all edges and at 300mm centres across the middle. Use stainless steel or coated screws designed for backer board — standard plasterboard screws will corrode. A 1200×800mm board typically needs 20-25 screws at 250mm centres. Always countersink screw heads flush with the board surface.

Do I need to tape backer board joints?

Yes — all joints between backer boards must be taped with waterproof joint tape (usually a self-adhesive alkali-resistant mesh) and covered with waterproof tile adhesive or tanking compound. This creates a continuous waterproof surface. Internal corners should also be taped. Some systems use pre-formed corner pieces for a more reliable seal.

Do I need to prime backer board before tiling?

Most backer boards need a coat of primer (like BAL Prime APD or Mapei Eco Prim Grip) before tiling to ensure good adhesive bond. Check the specific board and adhesive manufacturer's instructions — some combinations don't require priming. Primer coverage is typically 0.1-0.15 L/m². Allow 1-2 hours drying time before tiling.

TradeCalculator

Tile Backer Board Calculator — Boards, Screws & Tape

Calculate tile backer board quantities for wet areas. Includes board count, screws at 200-300mm centres, waterproof tape, and primer.

Wall Area

Wet area walls

Floor Area

If using backer on floor

Board Size

Price Per Board (optional)

How We Calculate This

This calculator determines tile backer board quantities including fixings and waterproofing accessories for wet area installations.

The formula

Boards = Ceiling(Total area ÷ Board area × Wastage)

Screws = Total area × Screws per m² × Wastage

Tape = Boards × Joint length per board

For example, 8 m² shower walls with 1200×800mm boards: 8 ÷ 0.96 × 1.1 = 10 boards. Screws at 300mm: 8 × 12 = 96 screws. Tape: ~5 rolls.

Frequently Asked Questions

Related Calculators

Wall Tile Calculator

Calculate wall tiles, adhesive and grout for bathrooms and kitchens.

Tile Adhesive Calculator

Work out how much tile adhesive you need for floors and walls.

Grout Calculator

Calculate grout quantities based on tile size and joint width.

Shower Tray Fall Calculator

Calculate the correct fall gradient for a wet room or shower tray.

Bathroom Extraction Rate Calculator

Calculate the required extraction rate for bathroom ventilation.

Last updated: March 2026

All calculations are estimates. Verify with your supplier.